* Against the Giants (G1/G2/G3) - it feels like cheating, since it's actually three modules, but there is enough of a link between the three to justify it. One of my favorite D&D memories is the epic fight in the center room of the Hill Giant keep, where we barely survived.
* The Lost Island of Castanamir (C3) - A wonderful module. Loved the room portals, which made things very interesting for the party. The Gingwatzim were also a nice addition that added a lot of flavor, particular the naranzim.
* The Gauntlet (UK3) - Technically, this should also include The Sentinel (UK2) because the modules were a single story in two parts. Defending the keep against an entire attacking force (including a giant!) was very, very cool, and the final encounter was well done.
* Treasure Hunt (N4) - 0-level characters trapped on an island trying to escape, reaching 1st level in the process. Written by Aaron Allston (who has moved on to bigger and better-paying gigs), this was very well done.
* The Hall of the Rainbow Mage (Necromancer Games G3) - Perhaps the pinnacle of "3rd edition adventures, 1st edition feel". I DM'd this module instead of playing it, but I think both the players and myself had a lot of fun.